Apparatus for dewatering granular material

ABSTRACT

Apparatus for separating granular material from water in which it has been carried, as in a hydraulic conveyor or the like, said apparatus including a hopper to receive material laden water, said hopper having an open bottom of substantial area, dewatering means surrounding the lower end portion of the hopper which is so constructed that the hydrostatic pressure of water in the hopper causes water to flow around the bottom edge of the hopper, through material arresting screens, and through overflow water outlets in the dewatering means, and granular material discharge means below the hopper and the dewatering means for removing dewatered material from the hopper through an outlet opening. Auxiliary external dewatering units are located adjacent the outlet opening, and in the top of the hopper is means for discharging water from above the level of material in the hopper. The apparatus is especially constructed to handle bottom furnace ash from a high capacity coal fired steam boiler, but may also be used for gravel or the like.

United States Patent [72] Inventor Edgar B. Tolman Winnetka, Ill. [21] Appl. No. 808,427 [22] Filed Mar. 19, 1969 45] Patented Nov. 2, 1971 [73] Assignee United Conveyor Corporation [54] APPARATUS FOR DEWATERING GRANULAR [56] References Cited UNITED STATES PATENTS 1,881,712 10/1932 Laughlin 210/311 X 1,935,642 11/1933 Laughlin 210/311 X 2,325,257 7/19 43 Loker 210/311 2,860,786 11/1958 Kittredge ..I.Q 3,399,715 9/1968 Ciaffone ABSTRACT: Apparatus for separating granular material from water in which it has been carried, as in a hydraulic conveyor or the like, said apparatus including a hopper to receive material laden water, said hopper having an open bottom of substantial area, dewatering means surrounding the lower end portion of the hopper which is so constructed that the hydrostatic pressure of water in the hopper causes water to flow around the bottom edge of the hopper, through material arresting screens, and through overflow water outlets in the dewatering means, and granular material discharge means below the hopper and the dewatering means for removing dewatered material from the hopper through an outlet opening. Auxiliary external dewatering units are located adjacent the outlet opening, and in the top of the hopper is means for discharging water from above the level of material in the hopper. The apparatus is especially constructed to handle bottom furnace ash from a high capacity coal fired steam boiler, but may also be used for gravel or the like.

APPARATUS FOR DEWATERIN G GRANULAR MATERIAL BACKGROUND OF THE INVENTION High steaming capacity coal fired boilers used in modern electrical generating plants produce several tons of ash a day, most of which drops out of the furnace in white hot or molten condition and falls into a water filled ashpit hopper in which it is quenched. The quenched ash, herein called bottom furnace ash," is a granular material much like coarse gravel and requires similar handling methods. Commonly the bottom furnace ash leaves the ashpit in a hydraulic conveyor system which delivers the ash laden water to a large hopperlike tank where the ash must be dewatered-Le, separated from the conveying water-before being loaded onto a conveyor belt or into railroad cars for transportation to a disposal site.

The quenched ash is of various sizes and includes some very fine material which must be allowed to settle. To avoid turbulence the tank is filled with water before ash-laden conveying water is directed into it. Conveying water flows axially downwardly into the water in the tank and rises slowly toward the periphery where water constantly flows over the edge of the tank, which thus acts as a continuous overflow weir and is so designated herein. This allows all but the very finest ash to settle in the tank. Ash is allowed to accumulate in the tank until it reaches a maximum permissible level which is at the bottom of vertically disposed decanting units that extend downwardly along the tank wall from the overflow weir. The water must then be drained offin a manner that will not allow ash to pas out with it. Large prior art tanks require several hours for water removal, despite the obvious economic advantage in minimizing this time to reduce the number of tanks required for a power plant. About an hour of standing time is usually allowed to let the fine ash settle out of the water at the top of the tank, leaving a large volume of top water that is practically free of ash; and that can be drawn off quickly through the decanting units which commonly extend downwardly 3 to feet from the weir. As the top water is decanted, or immediately afterward, the water remaining in the ash is removed so the ash delivered to the removal conveyance is substantially water-free, thus minimizing weight and spillage.

Heretofore, it has been customary to mount dewatering units on the inside of the tank wall with vertically spaced openings into the wet ash about 2-feet apart. The openings are shielded so that the water rises behind the shields and reaches an overflow orifice through which it is discharged from the tank. The wall of the tank defines a cylindrical upper portion and a frustoconical lower portion, and the dewatering units are located in both such portions.

This has been unsatisfactory for several reasons. First, the units take up considerable space and therefore reduce storage capacity. Second, they obstruct the free flow of dewatered ash from the tank when the tank is unloaded. Third, as the water level in the tank drops the dewatering capacity is progressively reduced as fewer and fewer units are below water.

For economy of operation a single dewatering unit should be capable of dewatering a large quantity of ash in a relatively short time and with sufficient thoroughness that the water can be returned to the conveyor system and reused. The total time required for dewatering the ash, discharging the ash and cleaning the tank should be minimum.

SUMMARY OF THE INVENTION The present invention provides an apparatus for dewatering bottom furnace ash conveyed from a coal burning furnace in a hydraulic conveyor, and the apparatus is capable of handling ash faster and with more efficient separation of water and ash then any dewatering apparatus heretofore known to applicant.

There are several reasons for the improved efficiency of the present apparatus. First, it has a completely unobstructed hopper with all dewatering units outside the hopper wall; so

there is nothing to interfere with the free flow of dewatered ash. Second, the hopper has a large open bottom with a single dewatering unit extending around the entire perimeter of the bottom end portion of the hopper so that the dewatering unit operates at full capacity as long as water is above the bottom edge of the hopper. Third, hydrostatic pressure causes the water to flow around the bottom edge of the hopper and up the outside of the hopper sidewall to water overflow outlets; and since the bottom furnace ash is relatively heavy it has little tendency to be carried around the l turn at the bottom edge of the hopper wall. By providing the water overflow outlets with flow regulating means, such as gate valves, to control the rate of flow of water through the outlets, the apparatus may function with almost no ash moving upwardly toward the drains.

Fourth, in order to arrest ash which might otherwise rise into the dewatering unit a simple horizontal screen extends between the hopper wall and the dewatering unit wall a short distance above the lower end of the hopper wall. The principal function of the screen is to hold the ash down so it acts like a filter bed through which the water passes to the outlets. The screen is especially important because the removal of water from the hopper may cause avalanching of ash which would rise into the dewatering unit were it not for the screen. Most ash arrested under the screen drops off by gravity, and any residue is easily washed off with a hose.

Since prior art dewatering units were mounted inside the tank wall they were relatively inaccessible for purposes of cleaning ash from them, so that in addition to a relatively slow rate of dewatering a complete cycle was lengthened inordinately because of the difficulty of cleaning the dewatering units. In the present apparatus all the dewatering elements were readily accessible from outside the hopper, and may be cleaned very rapidly with a hose when necessary.

The word "hopper" is used herein broadly to mean a chamber in which material is stored temporarily and then released through the lower end.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view, partially in section, illustrating the dewatering apparatus of the present invention;

FIG. 2 is a vertical central sectional view of an enlarged scale showing the lower end of the hopper, the main dewatering means and the discharge means of the dewatering unit;

FIG. 3 is a fragmentary and elevational view viewing FIG. 4 from the left;

FIG. 4 is a fragmentary sectional view taken substantially as indicated along the line 4-4 of FIG. 3:;

FIG. 5 is a fragmentary side elevational view on a reduced scale taken substantially as indicated along the line 5-5 of FIG. 2;

FIG. 6 is a fragmentary section on an enlarged scale taken substantially as illustrated along the line 6-6 of FIG. 2; and

FIG. 7 is a fragmentary sectional view on an enlarged scale taken substantially as illustrated along the line 7-7 of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings in greater detail, and referring first to FIG. 1, the dewatering apparatus of the present invention consists generally of a hopper, indicated generally at 10; dewatering means, indicated generally at 11; ash discharge means, indicated generally at 12; auxiliary dewatering means, indicated generally at 13; means indicated generally at 14 for removing water from above the maximum level of ash A in the hopper; and inlet means 15 for feeding ash-laden water Al into the hopper.

Describing the various components of the dewatering apparatus more specifically, the hopper 10 is defined by a continuous sidewall, indicated generally at 16, which includes a cylindrical upper portion 16a and a frustoconical lower portion 16b that terminates in an open lower end 17 of substantial area. The hopper in a typical moderate sized commercial installation has a cylindrical upper portion approximately 24- feet high and 35-feet inside diameter, and a frustoconical lower portion about -feet high with a bottom opening about 8 feet in diameter.

Referring now particularly to FIG. 2, the dewatering means 11 and the ash discharge means 12 include a unitary body structure the upper portion of which provides the dewatering means and the lower portion of which provides an ash discharge chamber. A confining wall, indicated generally at 18, includes a cylindrical portion 18a and a frustoconical lower portion 18b with the upper edge 19 of the confining wall continuously sealed to the hopper wall 16b adjacent the open bottom 17 to provide a chamber 20 which entirely surrounds the lower end portion of the hopper. The bottom of the chamber 20 is defined by ash arresting means in the form of an annular transverse screen 21 which is positioned a very short distance above the open bottom 17 of the hopper, and water outlet means 22 consists of pipes which have open upper ends 22a within the chamber 20 so that water in the ash-filled hopper is forced by hydrostatic pressure around the lower end 17 of the hopper, upwardly through the ash arresting screen 21, and through the water outlet pipes 22. Rate of outflow of water through pipes 22 can be regulated by flow control means in the form of gate valves 22b. In the upper portion 18a of the confining wall 13 is a plurality of cleanout openings provided with closures 180. Because of the fact that the water entering the chamber 20 must flow upwardly for a short distance between the lower end 17 of the hopper and the screens 21, very little ash is caught on the screens, and most of that which is caught can fall by gravity into the discharge means 12. Thus, practically the only cleanout work required is to occasionally remove the closures 180 from the cleanout openings and sluice down the screens 21 with water from a hose.

As best seen in FIG. 1, the water from the outlet pipes 22 flows into a drain pipe 23 which joins a drain pipe 24 that receives water from the auxiliary dewatering means 13, and a gate valve 25 is used to control the start of a dewatering operation. Pipes 26a and 26b provide, respectively, a continuous drain and a controlled drain for the top water removal means 14, with a gate valve 26c in pipe 26b to control the start of decanting of top water. A pipe 27 drains a drip pan drain means which is below the ash discharge means and will be described hereinafter. Water from all the drains 23 through 27 enters a common return conduit 28 which returns it for reuse in the hydraulic conveyor system or connects with a disposal sewer.

Referring now particularly to FIGS. 2-5, the frustoconical area defined by the lower portion 18b of the confining wall 18 has its lower margin 18c sealed to the upper margin 29a of a continuous wall, indicated generally at 29, that defines an ash discharge chamber 30 of the ash removal means 12. The continuous wall 29 includes parallel vertical wall portions 31 and inclined wall portions 32 and 33 joined to form a closed lower end 34. At the lower end of the wall 32 is an ash discharge opening 35 which is surrounded by a closure seat 35a (see FIG. 2).

In addition to the ash discharge chamber 30, the ash discharge means 12 includes an external housing 36 which supports a hydraulic cylinder and piston unit 37 having a piston rod 38 on which is mounted a closure 39 which normally bears against the closure seat 35a of the ash discharge opening 35. Thus, by actuating the unit 37 to retract the piston rod 38, the closure 39 is moved to open the ash discharge opening 35 for the purpose of discharging ash from the hopper 10, the lower portion of the dewatering means 11 and from the the dewatering boxes below transverse ash arresting screens 43 which re supported on external carrier plates 44 and project through slots 45 in the walls of the dewatering boxes 40. Above the ash arresting screens 43 the dewatering boxes 40 are provided with water outlets 46 through which water enters the drain pipe 24.

In the upper end of the hopper 10, above the maximum level of ash A, the top water removal means 14 includes a continuous channel 47 through which water that overflows the continuous weir 47a (defined by the top edge of the hopper) enters the drainpipe 26a, and one or more water decanting units 48 through which top water enters the drainpipe 26b. The channel 47 and the top water decanting unit 48 are of conventional structure and will not be described in detail.

Ash-laden water A1 from a hydraulic conveyor system enters the hopper 10 through the infeed means 15 which is supported on beams 15a and consists of an inlet pipe 49 on the vertical axis of the hopper, an open end cylinder 50 surrounding the pipe and an ash deflector plate 51 suspended in the cylinder 50 beneath inlet pipe 49 on brackets 51a. The cylinder 50 and deflector plate cooperate to reduce turbulence and to spread ash and water more or less uniformly around the hopper and prevent it from piling up in the middle.

Ash which passes through the ash discharge opening 35 at the bottom of the discharge chamber 30 drops through the outfeed pipe 52, either directly into railway gondola cars or dump trucks, or onto a belt conveyor which in turn loads it into cars or conveys it directly to a disposal dump site.

Since the closure 39 does not make a watertight seal against the closure seat 350, water leaks between the seat 350 and the closure 39 and drops into a drip pan 53 (FIG. 2) from which it enters the drip pan drainpipe 27. The drip pan 53 is pivotally mounted at 53a and is held in the operative position of FIG. 2 by a pair of counterweights 54. A small air motor 55 may pivot the drip pan 53 downwardly into the outfeed pipe 52 so that it does not obstruct flow of ash through the outfeed pipe.

A normal cycle for the dewatering apparatus of the present invention requires that the apparatus first be filled with water to the overflow weir 47a so that ash-laden water from the inlet pipe 49 enters the hopper with very little turbulence and ash may start to settle immediately to the bottom. This requires, of course, that the gate valve 26c of the decanting drainpipe 26b be closed, and that the gate valve 25 which controls the flow of water through the dewatering means 11 and the auxiliary dewatering means 13 also be closed. The flow of ash-laden water into the dewatering apparatus continues until the level of ash A in the apparatus is just below the bottom end of the decanting unit 48, at which time the flow of ash-laden water to the apparatus is stopped,

As previously indicated in the discussion of Background of the Invention the ash and water in the dewatering apparatus is permitted to stand for about an hour so that fine ash may settle out of the water which is in the top of the tank above the level of the ash A. The gate valve 26c is then opened to permit all water above the ash to leave the apparatus through the decanting unit 48, and at the same time or immediately thereafter the gate valve 25 is opened to permit water in the ash A to leave the apparatus through the dewatering means 11 and the auxiliary dewatering means 13. During all this time, of course, a small amount of water continues to leak out the bottom of the apparatus between the closure seat 35a and the closure 39 onto the drip pan 33 and through the drip pan drain 27.

As soon as all water is removed from the apparatus the air motor 55 is operated to pivot the drip pan drain 53 out of the way and the closure 39 is then moved away from the discharge opening 35 by operation of the hydraulic cylinder and piston unit 37. These may be separately controlled, or may be sequentially operated by a single control switch. In order to avoid delay in the discharge of dewatered ash, means (not shown) is preferably provided in the return conduit 28 for determining when flow of water into the conduit has stopped. This may take the form of a transparent visual sight gauge in the return conduit or it may consist of electronic sensing means. In the latter event, of course, operation of the air motor 55 and the hydraulic cylinder and piston unit 37 may be triggered automatically by the sensing means.

it is also apparent that the entire cycle may be made automatic by providing sensing means to determine when the level of water in the apparatus is high enough to begin feeding ashladen water through the pipe 49, and by further sensing means to determine when the level of ash in the hopper has reached the maximum permissible level. The former sensing means may be used to start the flow of ash-laden water through the inlet pipe 49, and the latter sensing means may be used to terminate such flow and open the gate valves 26c and 25. Further sensing means may also be provided for determining when all dewatered ash is discharged from the apparatus, and such sensing means may be used to close the gate valves 26c and 25 and to start a flow of water into the dewatering apparatus for the start of a new cycle. in the latter case a manual override must be provided so that a new cycle will not start automatically upon those occasions when the dewatering units are to be checked and cleaned.

The foregoing detailed description is given for clearness of understanding only and no unnecessary limitations should be understood therefrom as modifications will be obvious to those skilled in the art.

I claim:

1. Apparatus for dewatering granular material to separate it from water in which it is carried, said apparatus comprising, in combination:

a continuous sidewall defining a hopper which has an open bottom of substantial area;

means for feeding water laden with granular material into the top of the hopper; dewatering means associated with the open bottom of the hopper, said dewatering means including confining wall means outside the lower end portion only of the hopper sidewall and in spaced relationship thereto, said confining wall means having a margin continuously connected to the exterior of the hopper to provide a closed dewatering chamber into which the hydrostatic pressure of the water in the hopper causes water to rise after flowing around the bottom of the hopper sidewall, water outlet means for discharging water from the chamber, and granular material arresting means between the hopper and the water outlet means for effectively preventing granular material from entering said water outlet means; and

granular material discharge means below said dewatering means, said granular material discharge means including a continuous wall defining a discharge chamber which tapers toward its lower end, a discharge opening in said wall adjacent said lower end, a closure normally blocking said opening, and means for selectively moving said closure to permit granular material to pass through said opening.

2. The apparatus of claim l which includes auxiliary dewatering means associated with the discharge means, said auxiliary dewatering means comprising an external dewatering box mounted on said continuous wall, an opening in said continuous wall communicating with said box to permit water to flow into the latter, auxiliary water outlet means for discharging water from the box, and auxiliary granular material arresting means between the discharge chamber and said auxiliary water outlet means for effectively preventing granular material from entering said auxiliary water outlet means.

3. The apparatus of claim 2 which includes valve means for selectively preventing or permitting discharge of water from the dewatering means and the auxiliary dewatering means.

4. The apparatus of claim 2 in which the auxiliary granular material arresting means for the dewatering box comprises a screen mounted in the box between the communicating opening and the water outlet means.

5. The apparatus of claim 2 in which said continuous wall includes a vertical portion, and in which the dewatering box is mounted on said vertical portion.

6. The apparatus of claim 5 in which said continuous wall includes parallel vertical walls and an inclined wall, in which there is a dewatering box on each vertical wall, and in which the discharge opening is in said inclined wall.

7. The apparatus of claim 1 in which the confining wall means of the dewatering means entirely surrounds the lower end portion of the hopper sidewall.

8. The apparatus of claim 1 in which the confining wall means is generally upright and has an upper margin continuously connected to the hopper sidewall.

9. The apparatus of claim 1 in which the granular material arresting means comprises a transverse screen across the entire bottom of the closed chamber.

10. The apparatus of claim 1 in which the dewatering means and the granular material discharge means comprise a unit in which the lower margin of the confining wall and the upper margin of the continuous wall are sealed to one another.

11. The apparatus of claim 1 in which the hopper sidewall defines a cylindrical upper portion and a frustoconical lower portion, in which the confining wall of the dewatering means is concentric to the hopper sidewall and has an upper margin continuously connected to said sidewall to close the top of the chamber, and in which the lower margin of the confining wall and the upper margin of the continuous wall are sealed to one another.

12. The apparatus of claim 11 in which. the continuous wall of the discharge means includes a vertical portion and an inclined portion, auxiliary dewatering means is mounted on the outside of said vertical portion, and the discharge opening is in said inclined portion.

13. The apparatus of claim 12 in which the auxiliary dewatering means comprises an external dewatering box mounted on said vertical wall portion, an opening in said vertical wall portion communicating with said box to permit water to flow into the latter, auxiliary water outlet means for discharging water from the box, and auxiliary granular material arresting means between the discharge chamber and said auxiliary water outlet means for effectively preventing granular material from entering said water auxiliary outlet means.

14. The apparatus of claim 13 in which the auxiliary granular material arresting means for the dewatering box comprises a screen mounted in the box between the communicating opening and the auxiliary water outlet means.

15. The apparatus of claim 12 in which the continuous wall of the discharge means includes parallel vertical portions and an auxiliary dewatering means is mounted on the outside of each of said vertical portions.

16. The apparatus of claim 1 in which the water outlet means for the chamber of the dewatering means includes means for controlling the rate at which water may leave the chamber. 

2. The apparatus of claim 1 which includes auxiliary dewatering means associated with the discharge means, said auxiliary dewatering means comprising an external dewatering box mounted on said continuous wall, an opening in said continuous wall communicating with said box to permit water to flow into the latter, auxiliary water outlet means for discharging water from the box, and auxiliary granular material arresting means between the discharge chamber and said auxiliary water outlet means for effectively preventing granular material from entering said auxiliary water outlet means.
 3. The apparatus of claim 2 which includes valve means for selectively preventing or permitting discharge of water from the dewatering means and the auxiliary dewatering means.
 4. The apparatus of claim 2 in which the auxiliary granular material arresting means for the dewatering box comprises a screen mounted in the box between the communicating opening and the water outlet means.
 5. The apparatus of claim 2 in which said continuous wall includes a vertical portion, and in which the dewatering box is mounted on said vertical portion.
 6. The apparatus of claim 5 in which said continuous wall includes parallel vertical walls and an inclined wall, in which there is a dewatering box on each vertical wall, and in which the discharge opening is in said inclined wall.
 7. The apparatus of claim 1 in which the confining wall means of the dewatering means entirely surrounds the lower end portion of the hopper sidewall.
 8. The apparatus of claim 1 in which the confining wall means is generally upright and has an upper margin continuously connected to the hopper sidewall.
 9. The apparatus of claim 1 in which the granular material arresting means comprises a transverse screen across the entire bottom of the closed chamber.
 10. The apparatus of claim 1 in which the dewatering means and the granular material discharge means comprise a unit in which the lower margin of the confining wall and the upper margin of the continuous wall are sealed to one another.
 11. The apparatus of claim 1 in which the hopper sidewall defines a cylindrical upper portion and a frustoconical lower portion, in which the confining wall of the dewatering means is concentric to the hopper sidewall and has an upper margin continuously connected to said sidewall to close the top of the chamber, and in which the lower margin of the confining wall and the upper margin of the continuous wall are sealed to one another.
 12. The apparatus of claim 11 in which the continuous wall of the discharge means includes a vertical portion and an inclined portion, auxiliary dewatering means is mounted on the outside of said vertical portion, and the discharge opening is in said inclined portion.
 13. The apparatus of claim 12 in which the auxiliary dewatering means comprises an external dewatering box mounted on said vertical wall portion, an opening in said vertical wall portion communicating with said box to permit water to flow into the latter, auxiliary water outlet means for discharging water from the box, and auxiliary granular material arresting means between the discharge chamber and said auxiliary water outlet means for effectively preventing granular material from entering said water auxiliary outlet means.
 14. The apparatus of claim 13 in which the auxiliary granular material arresting means for the dewatering box comprises a screen mounted in the box between the communicating opening and the auxiliary water outlet means.
 15. The apparatus of claim 12 in which the continuous wall of the discharge means includes parallel vertical portions and an auxiliary dewatering means is mounted on the outside of each of said vertical portions.
 16. The apparatus of claim 1 in which the water outlet means for the chamber of the dewatering means includes means for controlling the rate at which water may leave the chamber. 